1. Field of the Invention
The present invention relates to a chip resistor provided with a thin-film resistor element, and also to a method of making the same.
2. Description of the Related Art
FIGS. 14 and 15 illustrate a chip resistor. The chip resistor 9 shown in these figures includes a insulating substrate 90, a pair of upper electrodes 91, a resistor element 92 connecting the paired upper electrodes 91, a pair of lower electrodes 93, a pair of end electrodes 94 connecting the upper electrodes 91 and the lower electrodes 93, a protective layer 95 covering the resistor element 92, and plating layers 96 for covering the electrodes 91, 93, 94.
The chip resistor 9, as shown in FIG. 16A, may be manufactured from a material substrate 9A which is formed with a plurality of dividing grooves 97A, 97B extending vertically and horizontally and setting a plurality of chip resistor forming regions 98 arranged vertically and horizontally.
Thick film printing may separately form the pair of upper electrodes 91, the resistor element 92, and the pair of lower electrodes 93 shown in FIGS. 14 and 15. For example, by printing and baking a material paste on the material substrate 9A, materials to be the upper electrode 91, the lower electrode 93 and the resistor element 92 can be collectively formed for the chip resistor-forming region 98 (see FIG. 16A). FIG. 16B shows an example of the material substrate 9A having an upper surface formed with a plurality of conductor materials 91A to be the upper electrodes 91. At a final stage, the material substrate is cut along the dividing grooves to provide separate chip resistors 9.
In thick film printing, lead glass paste dispersed with conductor particles is generally used as a material paste. However, considering environmental problems, it is undesirable to use a lead-contained glass paste.
The use of the material substrate 9A provided with dividing grooves 97A, 97B shown in FIG. 16A may cause the following problems due to miniaturization of the chip.
A first problem is caused by the material paste flowing into the dividing grooves 97A, 97B. In the material paste printing, the material paste may flow into the dividing groove 97A, 97B. Referring to FIG. 17, when the material paste for the upper electrode flows into the dividing groove 97A, the conductor materials 91A adjacent in the extending direction of the dividing groove 97A may be electrically connected to each other. After the upper surface of the material substrate 9A is formed with a resistor element 92, the resistance of the resistor element 92 is measured. Then, the resistance of the resistor element 92 is adjusted. In the measurement of the resistance, the conductor element 91A is held in contact with a probe P. Thus, with the adjacent conductor materials 91A connected electrically, the resistor element 92 connecting between the conductor materials 91A completes a parallel circuit, which impedes proper measurement of the resistance of the resistor element 92. In particular, the miniaturization of the chip causes a distance reduction between the adjacent upper electrodes 91 (the conductor materials 91A), which tends to lead to disadvantages described above. Further, the material paste flowing into the dividing groove 97A, 97B remains on a fringe of a product (chip resistor) when the material substrate 9A is divided along the dividing grooves 97A, 97B, which deteriorates the appearance.
To eliminate such disadvantages caused by the material paste flowing into the dividing grooves 97A, 97B, an excess may be removed by etching after baking the material paste. However, the miniaturization of the chip leads to a width reduction of the dividing grooves 97A, 97B, which impedes the removal of the excess remaining in the dividing grooves 97A, 97B. Further, the additional process of etching results in a decline in production efficiency.
A second problem is an increase in rejection rates in mounting. When the material substrate 9A is divided along the dividing grooves 97A, 97B with external force, the chip may be chipped off and deteriorate in shape. In particular, the small chip is greatly influenced in shape by being chipped off, which tends to lead to the increase in rejection rates in mounting.
A third problem is a decrease in yielding percentage. As the chip is downsized, the material substrate 9A needs to be reduced in thickness. In that case, the dividing grooves 97A, 97B formed on the material substrate 9A may contribute to generation of a crack on the material substrate 9A in such steps as printing or baking the material paste. As a result, the increase in rejection rate leads to the decrease in yielding percentage, which increases manufacturing costs.